Customers on any of these roads may pay tolls from pre-paid accounts using a FasTrak transponder — a pocket-sized radio transmission device mounted to the inside of their vehicle’s windshield. The I-110 Express Lanes are free to carpools with two or more people but the vehicle must have a transponder. The I-10 and 91 Express Lanes are free to carpools with three or more people but the vehicle must have a transponder.